There are numerous applications with the need for extremely miniaturized motors. For example, in consumer products extremely small, low weight, low power consumption and inexpensive motors are typically requested. The motion range is often in the order of millimeters and with a requested accuracy of micrometers. A number of performance properties are typically requested, e.g. high speed, silent movement, low power consumption, easily controlled positioning and high positioning accuracy, which to some extent are contradictory.
In order to reach highly accurate positioning that at the same time is relatively easily controlled, different motion mechanisms are selected, such as “walking” mechanisms, stick-slip mechanisms, “inertial” positioning or stepping mechanisms. Common for most devices operating according to such principles is that they involve a high degree of static contacting between an actuator and a body to be moved. The position accuracy relies to a large extent on this static contacting. However, the speed is often relatively low, the devices often operate at sub-ultrasonic frequencies, which may make them noisy, and the power efficiency is relatively poor. A typical example of such a device is disclosed in the U.S. Pat. No. 6,798,117.
In order to reach high speed and high power efficiency, other motion mechanisms are typically utilized. Common for most of these mechanisms is that they use mechanical resonances in one way or another. The actuator and/or body to be moved is thereby excited into vibration, thereby typically reducing the experienced friction between the actuator and the body to be moved. The power efficiency becomes generally high. In most cases, the geometrical dimensions are such that the selected frequencies are within the ultra-sonic range, which makes the operation relatively silent for human beings. However, positioning accuracy and/or easy control of e.g. start and stop sequences are difficult to achieve. A typical example of such a device is disclosed in the US patent application 2005/0073219.
In U.S. Pat. No. 5,345,137, an ultrasonic vibrator design is disclosed, which allows for a multi-dimensional motion of an actuating element. In U.S. Pat. No. 6,066,911, an ultrasonic driving element is disclosed, which has many similarities with the elements presented in U.S. Pat. No. 5,345,137. However, here a number of actuating elements positioned one after the other are used for achieving a combined ultrasonic frequency motion.
It has later been shown in the U.S. Pat. No. 6,798,117 that a similar main geometrical design as in U.S. Pat. No. 6,066,911 instead advantageously can be used for a fine-controlled walking mechanism. However, in order to achieve good operation properties, different detail designs are to prefer. Still, there are no prior art electromechanical actuators that operates well both with a fine-positioning mechanism and with a resonant high-speed mechanism.